The present invention generally relates to fixtures for the chemical-mechanical (chem-mech) polishing of semiconductor device wafers and, more particularly, to such a fixture adapted to eliminate non-uniform removal of material due to non-uniform loading or flexing of the wafer.
The prior art has focused attention on problems, including non-uniformity of polishing, associated work pieces including semiconductor device wafers. U.S. Pat. No. 3,518,798, issued to Stephen A. Boettcher on Jul. 7, 1970 discloses a polishing machine having a load plate for pressing work pieces to be polished against a polishing wheel. Pressure is applied to the load plate at a location intermediate the center and outer periphery of the load plate, to help reduce the peak deflection of the load plate. Non-uniform polishing within the interior of each work piece is not directly addressed. U.S. Pat. No. 4,313,284, issued to Robert J. Walsh on Feb. 2, 1982 describes the mounting of a number of semiconductor wafers onto a deformable carrier which, in turn, is mounted through a resilient device to a pressure plate in engagement with a bowed polishing surface. The carrier is deformed to match approximately the polishing surface curvature to reduce non-uniformity of the removal of wafer material.
Thus the cited art, in various ways, applies predetermined non-uniform pressure to work piece or to wafer carriers in attempts to compensate for inherent polishing forces that are non-uniformly impressed across the work piece face and which would result in non-uniform removal of wafer material in the absence of some sort of force compensation. That is, in the absence of force compensation, one or more regions of a wafer would be excessively eroded or "dished" during polishing relative to other regions. In each cited prior art instance, a certain degree of design complexity must be tolerated in order to provide the compensatory forces necessary to counteract the inherent polishing forces that otherwise would result in non-uniform removal of wafer material.